Voltage control and stabilizing circuits



Jan. 3, 1950 G. HERZOG 2,493,536

VOLTAGE CONTROL AND STBILIZING CIRCUITS Original Filed March 17, 1945 Mmmm x5' Patented Jan. 3, 1950 VOLTAGE CONTROL AND sTABILIzING CIRCUITS Gerhard HerzogrHouston, Tex., "assig'nor to The Texas Company, New York, N. Y, `a corporation of Delaware Original appiicatin Maren 17', 1945, 44 serial ing. 583,315. Divided and this application January 29, 1949, seria1N0.73,571

The present Vinvention relates to improvements in connection with means for the investigation of the intensity of radiations and more -particularly of the nature and properties of formations, such as those surrounding a bore or well, as oil Wells and bore-holes, and more particularly for the investigation of radioactive properties of these formations, either natural or as modified or inuenced by therapplication of various types of radiation thereto.

This is a division of my copending application Serial No. 583,315, led March 17, 1945.

In radioactivity Well-logging, it has heretofore been proposed to employ for the exploration of the oil Wells or bore-holes, instruments containing radiation detectors of various types, such as ionization chambers, in which a continuous current is derived from the detector, the amount of the current varying as a function of the intensity of the radiations from the formations encountered by the instrument; and also to use detectors of the pulse-,producing or counter type, from which, instead of continuous currents, `cur rent pulses are derived, the frequency of which is a function of the intensity of the radiation from the formations traversed by the instrument. In the use of detectors of the counter type, depending upon specific details of construction and conditions of operation, the size or amplitude of the pulses may be approximately proportional to the initial ionization produced as a result of the radiations from the formations, in which casethe detector is designated a proportional counter; or it may be substantially inde'- pendent of such initial ionization, in which case it may be designated as a non-proportional counter. The Well-known Geiger-Mller counter is a detector of the latter type, as are also the high efficiency counters or detectors disclosed in the U. S; Letters Patent of myself and another, No. 2,397,073, granted March 19, 1946 and in the U. S. Letters Patent of Donald G. C. Hare, No. 2,397,071, granted March 19, 1946.

Asy is Well-known, considerable variatidns temperature are found in oil wells or bore holes, particularly in the case of deeper Wells, Awhich may extend to depths of two to three miles, or even somewhatdeeper. Temperatures as high as ,200 to V240 F. may be encountered. In radio'- 7 activity Well-logging with devices using the ionizatln chamber or continuous current output type of radiation detector, it has been found impiactical to log vvells inflvvhich higher temperatures, say above about 170 F., are" encountered,

2 as ,such devices apparently become ineiective and Finaccurate under such conditions,

It has noyv been found thaty radioactivity loggingof Wells, even at the highest temperatures which have been encountered, may be `satisfactorily accomplished, lemploying radiation detectors Aof the counter type, is known, such counters, for non-proportional operation, have imposed upon them a relatively high directeurrent voltage and there is 'a limited range of voltages, known as the operating plateau, in which theradiation results pulses which areY practically independent ofthe, amount of initial ionization. The vvoltage for, operation of the counter `-is selected from Within this plateau.

It has been found that the proper` voltage for operation of .such counters varies with thetem'- perature of the counter, iricreasingwith increase f., i'rliratef. Thus a pulier. Smiles a Geig-Miiller counter pr, the high @1i-menor counters of the patents of Hare and myself h eretofore referred tokvvhexn properly constructed, may operate satisfactorily vvhenha voltageof say 1000 volts isdinpressedhupon Vit and the counter is atordinary room temperature, say about E". 4It canb raised temperature toi some ex- 'tent and vstill operatebeasonably satisfactorily at 1000 vlts. Hovvever, the voltages constituting the liinits of the. rangeY or plateau Within which the cinterinaybe properly operated,rise as` the temperature rises. '\Ifhus; if the operating voltage is at an intermediate point on the pla;- teau, soine temperature rise may be encountered beforelit is belowl the minimum voltage for proper operation. In Order that the counter may be properly operated at the higher temperatures cot'ed in oil vvll's, `I have found *that4 the voltage inpressedwuponnthe counter should be increased with increase in temperature and have d'fiseiibineansv vvvherby Athis may be, automatically effected; Thus I have` found that with a high iliciiency detector such ,as those above refei'jrd to, for vvhuiclnzthe operating voltage of the detector is abinitl g; volts at '70 F., it should be raisedA to about 1,950,7voltsvyvhen thetemperatureris's to about 212 F; ^`The specific figures given are illustrative and both the proper operat-A ing voltages and the amount of voltage, ,in\crease for. the yfi'lciegase temperature specified may vary with different detectors. TheJ iigures given those found in connection with ,they operationof a detector sughas that Vdescribed in the patent of Hare, No. 2,697,071; above referred to;

In ca ngtout the present invention; rI prothe logging instrument containing Vthe radiation detector, a source of direct current Voltage at a higher potential than that which is to be impressed upon the detector and take from this source a reduced voltage for application to the detector, this reduced voltage being automatically varied'with variations in temperature encountered by the instrument. By way of illustration suitable means for carrying out the present invention are shown in the accompanying drawings, in which Fig. 1 illustrates diagrammatically aninstrument embodying Ymeans for carrying out the present invention, shown in a cased bore hole;

Fig. 2 illustrates in part diagrammatically, partly in perspective, an alternative arrangement for securing the proper variation in the voltage to be applied to the counter with variations in temperature; and

Fig. 3 represents diagrammatically a portion of the circuits employed in connection with the arrangement of Fig. 2.

' Referring to Fig.v 1 a fragmentary part of a bore-hole is shown, in which the numeral 5 desighates a portion ofthe `formation surrounding a bore hole and Sethe casing. The numeral 'I'desig- Ynates the housing of the logging instrument, Vwhich is suspended by a cable 8 fromv thesurface.

'Ihis cable may suitably be of the shielded single conductor type, the :internal conductor being 'designated by,V the numeralf 9,' and the shield, f

cable'the necessary current, for example, alowfrequency -alternating currentfo'r direct current, for operating the instruments in the well. Likewise, means are provided, at the surface for the necessary amplification Y and recording of signals derived from the radiation detectorV in the ,'well, preferably in correlation witht'the recordings of the depth of the instrument. These, which may be of types known in the art, are not illustrated. y

The current from the power source at the sur- Y Vface, whichmay be an alternating current, for

example, is applied tothe cable conductor 9, the

shield I0 serving as a return or ground. The

housing isl so attached tov thecable that thereis Van electrical connectionbetween it and the cable shield IIJ, so that the wall of the housing may be conveniently used as a returnor ground for the electrical instrumentswithin the housing, which are diagrammaticallyillustrated. V

Y Within the housing, a conductor II takes current from the cable conductor 9 and is connected to a suitable lter I2, which permits Apassage ofV the power current supplied to the instrument, for example'a 220 volt, 60 cycle current, but blocks the passage of the signals derived from the detector or'counter. From the filter the power currentis supplied through conductor I toa power pack I5, inV which provision is madefor transforming and rect/ifying theV current to YsecureV the desired voltages of direct'current for operation ofthe detector and the amplifiers within the instrument housing. A connection I6V is provided from the power pack to the housing of the instrument for the grounding or return of the power current and a suitable connection l I1 is provided :from the 4 power pack to the instrument housing as the ground connection for the rectified currents produced within the power pack. Y

The numeral I8 designates the radiation detector, which is shown schematically by a representation of a counter having a central anode wire surrounded by a cylindrical cathode 20. The counter is completely closed and filled with a suitable gas or mixture of gases at low or sub-atmospheric pressure, as is known'in the art. While a counter of conventional type is shown for the purposes of illustration, I prefer to employ a high efliciency counter of the types described in the aforementioned Patent Nos. 2,397,073 and 2,397,071. Irrespective of the type of counter employed, it is preferred that it be of the selfquenching type; that is, that it should contain a Vgas mixture including a small proportion of an organic vapor, such as alcohol, petroleum ether, or the like, to facilitate quenching.

The power pack I5 delivers through the conductor 2I a rectified and preferably, stabilized direct current voltage at a substantially higher potential than that required for proper operation of the detector I8. Thus, with a detector requiring about 1000 voltsY for proper operation at normal temperatures, the power pack may deliver` to the line 2l a direct current voltage of say 1200 volts. These figures are, of course, for purposes of illustration only, although Yrepresenting conditions actually obtaining inpractical operations in 'some cases.

In order that the proper voltage may be applied to the counter, the necessary positive operating potential is impressed upon its anode I9 through conductors 22 and 22a. Conductor 22 is connected to a voltage divider shown for purposes of illustration as consisting of resistors 23 and 2t connected in series between the conductor ZI and the Vconductor 25 leading to the housing or ground. While only tworesistors 23V and 24 are illustrated, it will be understood that additional resistors may be interposed in the voltage divider, if desired, or either or both of the resistors 23 and 24 may be made up of more than one resistor in series.l Conductors 22 and 22a may be directly connected, if desired, or conductor 22 may pass to a preamplifier and quenching circuit 20,.which may be of any of the well-known types, which is connected through conductor 22a with the anode of the detector 2li. l Y

In accordance with the present invention, the resistors 23 and 24 aremade in whole or in part of materials having different temperature coefficients of resistance, so that, with rise in temperature, the resistance of resistor 2li increases more rapidly than that of resistor 23 'and thereby,

with constant voltage output from the power I include materials having negative temperature coeicients of resistance), say of 0.0004, or lower, such as constantan, maganin, Nichrome, graphite, or the like; and the-material having a' high temperature coefficient vof Aresistancefof which the resistor 24 may be made in whole or in part;

may be any of the known resistance materials,l suitably having a temperature coefcient of re-- sistance of0.003 or higher, such as copper, nickel, iron, silver, Phosphor bronze, or the like. The temperature coefficients of various resistance materials suitable for use are well-known, see, for example, Radio Engineers Handbook by Terman, New York, 1943, page 27.

For example, under the specific conditions hereinbefore referred to for purposes of illustration under normal atmospheric temperature, say about C., a proper operating voltage for the counter would be 1000 volts. With the direct current supplied through the line 2| at a voltage of 1200, resistors 23 and 24 would be in a ratio of 1:5. If now the instrument is brought into a region within the bore-hole in which the temperature is 100 C., the proper operating voltage for the counter rises to about 1050 volts and in order to secure this voltage, the ratio of the resistances of resistors 23 and 24 would be 1:7.

By using for the resistor 23 a material of practically zero coefficient of resistance, such as constantan, and by using nickel as the material for the resistor 24, the proper shift in voltage will be secured; and a sufliciently accurate approximation can be secured by using other materials, such as copper, silver, or Phosphor bronze for the resistance 24, or by using iron for a portion of that resistance, particularly if materials having negative coefficients of resistance, such as ohmax or carbon are employed in part or in whole for the resistance 23. As is readily apparent, there are a great number of variations which may be made with the knowledge of those skilled in the art. The total value or sum of the resistances of resistors 23 and 24 may vary widely and for practical purposes should be high enough to avoid excessive current drain on the high voltage supply. Thus the total resistance of resistors 23 and 24 may suitably be in the range from 0.25 to 1 megohm.

Since the resistors 23 and 24 are contained within the same instrument housing as the detector, they are subject to the same variations in temperature resulting from environmental changes and immediately and automatically compensate therefor.

The operating voltage for the detector, taken olf through the conductor 22, is impressed upon the anode I9 of the detector, the cathode 20 being connected to the housing I of the instrument, or in effect grounded, through the line 23. In use, ionizing particles resulting from the action of the radiations from the surrounding formations, such as gamma rays, either natural or induced, cause current pulses, which are transmitted through the conductor 22a. to a quenching and amplifying circuit 26.

The quenching and amplifying circuit 26 is not shown in detail, as it may be any suitable known quenching and amplifying circuits, preferably one yielding pulses of equalized amplitude, such as the circuits illustrated in Strong, Procedures in Experimental Physics, New York, 1944, pages 283 and 284. It is preferred, however, to employ the circuit shown in the application of Hare, Ser. No. 581,647, filed March 8, 1945, or that of the U. S. Letters Patent of Lord, No. 2,419,496, granted April 22, 1947. The necessary operating currents for the quenching and amplifying tubes are derived from the power pack I5, as through the connectors 21 and 28, and the connector 29 designates the connection for the quenching and amplifying circuit to the instrument housing or to ground.

The amplified pulses constituting the output of the `quenclfxing and amplifying circuit 26 pass. through .connector 3| to the transformer 32, through which the coupling to the conductor .9l of the cable 8 is eiected, and the ypulses im- Dressed thereupon.

As is readily apparent from the foregoing description, as the instrument housing moves through the bore-hole and encounters various temperatures, any variation in temperature will result in a corresponding variation in the voltage applied to the anode of the detector or counter. While the invention has been illustrated in connection with a counter in which a rise in temperature ofv from about 70 F. to about 212 F.

will require a change in operating voltage for most effective result of from 1000 volts to 1050 volts, the appropriate `operating voltage and variation of temperature will depend upon the spe. cie construction of the detector. These characteristics can be readily determined by suitable tests of the detector prior to use and the resist-- ances employed may be calculated accordingly.

Figs. 2 and 3 illustrate an alternative arrangement bywhich the variable voltage required in accordance with the present invention maybe secured. In these figures, numeral 2| designates the connection to the high voltage source corresponding to conductor 2| of Fig. 1; 22 designates the connection to the anode of the detector or to the quenching circuit 26, corresponding to con--l ductor 22 of Fig. l, and resistor 23 corresponds to a portion of the resistor 23 of Fig. 1. To secure the desired variation in resistance ratios, a potentiometer is employed, the resistance ratio being changed by movement of the tap on the poten tiometer by means of a temperature-responsive element, such as a bi-metallic spring or coil, such constructions being known in the art. As shown in Figs. 2 and 3, the stationary potentiometer disk 45 of suitable insulating material carries a resistor 46, one terminal 41 thereof being connected through conductor 48 to resistor 23. The other terminal 49 of resistor 46 is connected through conductor 50 to resistor 24', which corresponds to part of resistor 24 of Fig. l. Resistor 24 is grounded to the instrument housing in the same manner as is resistance 24 of Fig. 1.

A tap or contact spring 5|, which contacts the resistor 46, is mounted on a rotatable shaft 52, which passes through the potentiometer disk 45 and may be rotated relative thereto by the bimetallic coil 53, one end of which is secured to shaft 52 and the other end to a pin 54 secured to disk 45. Changes in temperature cause the bimetallic coil to rotate the shaft 5I and with it, the tap 5| or resistor 46. The tap 5I is connected through conductor 22' to the detector anode.

In the alternative form illustrated in Figs. 2 and 3, the resistors 23' and 24' may be made of materials of the same temperature coeicients of resistance. The potentiometer is operated through the temperature responsive spring 53 so that the ratio of the resistances in the circuit changes with increase in temperature in the desired proportion to secure the required change in voltage delivered to the detector through conductor 22'.

If desired, a source of radiation such as gamma rays, fast neutrons, or the like, properly shielded from the detector I8, may be included in the instrument housing with it, or may be associated therewith, and the radiations detected by the detector may result from or be induced by the radiations from such source. Thus the invention may be employed in logging gamma ray radiation from strata as Yinfluenced by bombardment by neu-` trons or other penetrating radiations, or'in logging induced neutron radiation, with proper modification of the detector, as Vknown in'the art. The invention may be employedy in other situations in which a radiation detector may be required to operate under varying temperature conditions; for example, in connection with the use of the thickness measuring device of Hare, reissue Patent No. 22,531, of August 22, 1944.

Although the invention has been illustrated in connection with certain embodimentsl thereof, it is not to be limited thereto, except in so far as such limitations are included in the accompanying claims. i f v I claim: Y

1. In'apparatus for radioactivity well logging, an instrument housing containing a` radiation detector of the counter type, a voltagedivider and means for supplying a high direct current poten tial thereto, a tap on said voltage divider connected to an electrode of said detector, and means for .varying the ratio of resistances in said voltage divider with changes in temperature whereby the potential applied to the detector electrode is varied to maintain effective operating conditions at varying temperatures.

2. In apparatus fordetecting and measuring radiation, a radiation detector` of the counter type, a voltage divider and means for supplying a high direct current potential thereto, a tap on said voltage divider connected to an electrode of said detector, and means subjected to substantially'the same temperature conditions as said detector'for varying the ratio of resistances in said voltage divider with changes in temperature and thereby varying the potential applied to the de tector electrode to maintain effective operating conditions atA varying temperatures.

A3. In apparatus for radioactivityrwell logging, an instrument housing containing a detector of radioactivity of the counter type, a voltage divider and means for supplying a high direct current potential thereto, and a tap for taking off an intermediate voltage from said voltage divider, said tap being connected with an electrodeof said de-g tector to impress a potential thereon, and means responsive to temperature changes within said housing for eiecting a relative movement of said tap and a resistor of said voltage divider to vary the ratio of the resistance in said voltage divider and therebyv vary the potential upon said Vdetector. Y Y v l Y 4. vIn apparatus for radioactivity well logging, an instrument housing containing a detector of radioactivity of theY counter type, a voltage divider and means for supplying a high direct current potential thereto, said voltage divider including a potentiometer having a resistor and a contact arm adapted to be moved over said resistor in contact therewith for taking off an intermediate voltage from said voltage divider, said arm being connected with an electrode of said detector to impress a potential thereon, a temperature-responsive element connected to said arm and responsive to temperature changes Within said housing for eiecting movement of said arm to vary the ratio of resistance in said voltage divider and thereby vary the potential upon said detector.

5. Apparatus as deiined in claim 4 in which the temperature-responsive element is a bimetallic coil having one end attached to said potentiometer arm and the other end attached to the casing of the potentiometer. Y

' GERHARD HERZOG.

No references cited. 

